Identification of 33 Rice Aquaporin Genes and Analysis of Their Expression and Function

Abstract

Plant aquaporins form a large protein family including plasma membrane-type (PIPs) and tonoplast-type aquaporins (TIPs), and facilitate osmotic water transport across membranes as a key physiological function. We identified 33 genes for aquaporins in the genome sequence of rice (Oryza sativa L. cv. Nipponbare). We investigated their expression levels in leaf blades, roots and anthers of rice (cv. Akitakomachi) using semi-quantitative reverse transcription-PCR (RT-PCR). At both early tillering (21 d after germination) and panicle formation (56 d) stages, six genes, including OsPIP2;4 and OsPIP2;5, were expressed predominantly in roots, while 14 genes, including OsPIP2;7 and OsTIP1;2, were found in leaf blades. Eight genes, such as OsPIP1;1 and OsTIP4;1, were evenly expressed in leaf blades, roots and anthers. Analysis by stopped-flow spectrophotometry revealed high water channel activity when OsPIP2;4 or OsPIP2;5 were expressed in yeast but not when OsPIP1;1 or OsPIP1;2 were expressed. Furthermore, the mRNA levels of OsPIP2;4 and OsPIP2;5 showed a clear diurnal fluctuation in roots; they showed a peak 3 h after the onset of light and dropped to a minimum 3 h after the onset of darkness. The mRNA levels of 10 genes including OsPIP2;4 and OsPIP2;5 markedly decreased in roots during chilling treatment and recovered after warming. The changes in mRNA levels during and after the chilling treatment were comparable with that of the bleeding sap volume. These results suggested the relationship between the root water uptake and mRNA levels of several aquaporins with high water channel activity, such as OsPIP2;4 and OsPIP2;5.

Water relations and an expression analysis of plasma membrane intrinsic proteins in sensitive and tolerant rice during chilling and recovery

“…Rice PIPs in control plants had large fluctuations in expression during a light/dark cycle (data not shown) confirming a previous report [7]. Thus we compared the changes in expression of all 11 PIPs in concurrent control plants without chilling treatment to the chilled plants both during chilling and after recovery.…”

“…Many reports have emphasized the changes in water relations because water homeostasis is essential for plant survival under this stress condition, and a significant symptom of chilling injury is shoot water deficit resulting from imbalance between water transport and transpiration [2]. It has been well documented that root water transport is sharply suppressed by exposure to low temperature in a number of species, including maize [3][4][5][6], rice [7], bean [8], spinach [9], aspen [10], cucumber and figleaf gourd [11,12]. Some studies have also demonstrated that a decrease in transpiration follows the reduction in root water flow [5,10].…”

“…Aquaporins have previously been reported to be involved in chilling responses [4,19] but only recently have comprehensive analysis of aquaporin expression at the mRNA level in response to low temperature been done. Techniques used were Northern blot, semi-quantitative reverse transcription (RT)-PCR and real-time RT-PCR using SYBR green dye in species such as Arabidopsis [20], maize [6] and rice [7]. Comparative analysis between cucumber (chilling sensitive) and figleaf gourd (chilling resistant) indicated that the decrease in cell hydraulic conductivity (Lp) at low temperature was associated with the open/close state of water channels [11,12].…”

“…Nipponbare were surveyed. Sakurai et al [7] recently reported the identification of 33 rice aquaporin genes (11 PIPs, 10 TIPs, 10 NIPs and 2 SIPs) by analysis of the rice genome. Hence, throughout this paper, we have used the aquaporin names as proposed by Sakurai et al [7].…”

“…Sakurai et al [7] recently reported the identification of 33 rice aquaporin genes (11 PIPs, 10 TIPs, 10 NIPs and 2 SIPs) by analysis of the rice genome. Hence, throughout this paper, we have used the aquaporin names as proposed by Sakurai et al [7]. We selected 4 PIP genes including 3 coding for functional water channel proteins (OsPIP1;1, OsPIP2;1 and OsPIP2;7) and a root-specific one (OsPIP2;3) for comparing the transcript expression level of Somewake and Wasetoitsu during chilling and recovery.…”